Paper pulp screen



Aug. 25, 1942.

N. w. JNssoN 2,293,978

PAPER PULP SCREEN Uriginal Filed Sept. l5, 1956 3 Sheets-Sheet l ILL Aug. 25, '1942. N. w. JNssoN 2,293,978

PAPER PULP SCREEN Original Filed Sept. l5, 1936 3 Sheets-Sheet 2 Aug. 2'5, 1942.

N. w. JNSSQN PAPE PULP SCREEN original Fild Sept. 15, 1936 3 Sheets-Sheet 3 Patented Aug. 25,1942

UNITED p STATES PATENT oFF-ICE Original application September 15, 1936, Serial No. 100,958. Divided and this application February 23, 1940, Serial No. 320,485. In Sweden` November 2, 1933 1 Claim.

'Ihis application.is a division of my co-pending application Serial Number 100,958 filed September 15, 1936.

The invention relates to an l apparatus for screening cellulosic pulp ,said apparatus being in several respects much simpler and more advantageous than apparatus hitherto used for producing cellulosic pulp products, for instance chemical and mechanical wood pulp, paper, cardboard and Wall board.

It has been found that a vibratory motion of a screening member under certain conditions creates a special eiect when screening suspensions of fibrous material which may or may notv be mixed with other solids.

In apparatus for straining paper pulp, it has been proposed to mount the frame and the strainer-plates constituting the inner vat, upon spring-supported bearings arranged at op'posite sides of the said vat, and to impart to the bearings on one side only thereof vibratory motions with the effect that the entire vat is caused to partake of a vibratory'movement about a longitudinal axis Which passes through the centre of inertia of the mass moved; the same actuating motions operating, in conjunction with the reactions of the bearing springs, to impart to the vat a to-and-fro altitudinal movement.

In carrying out the invention the suspension of fibrous material is led to one side of an elongated troughlike screen, extending in the.longi tudinal direction substantially horizontally from an inlet at one end to an outlet at the other end, and comprising inthe direction of ow first a relatively short portion extending steeply downward, and then as continuation thereof a portion, everywhere 'inclining less steeply to the Ihorizontal plane than the rst portion and from a lowest point successively rising to the outlet portion of the screen, said screen at its middle portion being united with means for vibrating the screen sides and carried on both sides by elastic, substantially vertically yielding means so that the inlet end as well as the outlet end of the screen perform orbital vibrations, liquid beneath the screen being vdam'med up and the screen thereby being at least partially surrounded by liquid on both sides. the fibres of a suspension and especially of the bres next to the screen, provided the vibration is of a suitable kind, is very remarkable. The explanation of this fact might not lie only in the motion of the fibres relatively to the screen,

which motion is very favourable to the intended treatmentlbut also in themotion of the libres relatively to the liquid of the suspension, especially near tothe screen.

VBy creating suitable conditions in the form of a suitable vibration, it has proved possible in most cases not only to transportv the libres along the vscreen but also to keep Athe screen free of coatings of fibrous material and in many cases even to keep the screen free of impurities,.for example, resins, of -the kind that often cause difficulties by accumulating on screen members.

It has proved suitable in certain cases to vary the period and amplitude of the vibrations of the screen. Thus, in some cases it has been suitable to impart to the screen very violent vibrations up to vand above 1000 a minute not going below 200 a minute. The amplitude of such vibrations should not exceed 8 mm. In other cases it has been Suitable to use vibrations of an amplitude of 4 to 16 mm. with the number of vibra-` tions per minute lnot exceeding 400 and not below 100. 'Ihe vibrating screen is preferably put into vibration by the direct actuation of a vibration member, in which the motion is created by electric, magnetic mechanical or pneumatic means. In such a case it is suitable, when treating the fibrous material, to control the vibrations of the screen by altering the electric frequency or the current strength or the air pressure or 'the air quantity in the vibration member or by adjusting the mechanical device so that a change of the speed-of vibration and/or the amplitude of the vibrations is obtained. In certain cases it has proved to be most advantageous if the screen has a uniform or almost uniform vibration, in other cases, again, itV has proved most advantageous to impart to the screen a vibration, which is different at different parts of the surface. It has proved suitable to supply to the screen a larger quantity of the suspension than can be ber, in which coarse particles are separated from The effect created by a vibration of the suspension. This screening member also may be constructed in accordance with the invention.

In several applications of the method according to the invention it has proved favourable to accelerate the passage through the screen by applying-an over-pressure above the suspension while it passes over the whole or over part of the Screen. It has also proved advantageous to accelerate the passage of the li'quid and of the suspension through the screen by producing partial vacuum under the surface of the screen.

Of course, it is possible and in certain cases it In all cases it is essential, that theI screening surface, a small or great part of it, is wholly surrounded by liquid. The special eiect described above can only be obtained by such a use of the liquid.

For dehydrating or concentrating the stuff for example from 0.20 to 5.0% a simple shaking trough having a curved screening surface may be used instead of a rotating draining drum. This entails saving of power, reducing losses of the stuff and simplified attendance.

In screening paper pulp, in separating knots from cellulose and in grading ground pulp or stui for the production of wall board and the like and in taking care of fibre occurring in slight quantities in waste water, apparatus of the above described kind may which improved results are obtained in comparison with apparatus used hithertofore.

The above described apparatus may be advantageously used for the purpose of depriving cellulosic pulp and other such brous mass of resin. The resin occurs .substantially in and on, the nest parts of the fibrous mass, and if the finest parts are removed by means of the invented apparatus a stuff is obtained, which has a considerably lower resin content than the stui has prior to the treatment. The separated quantity of ne cellulose fibers may amount to 10%-15% of the suspended matter, but should preferably be limited to 3%-5%.

In the case in which about 10-l5% of ne particles are separated, it may also be convenient to subject the stui thus separated, which is rich in resin, to a subsequent separation in an appa-i ratus of the described kind for the purpose of separating the main part of the said stuff of a lower resin content.

Onaccount of the direct shocking effect of the screen which is mild but which is repeated many times, to which effect the vparticles are subjected on account of the vibration of the screen a very complete releasing and separation of resin takes place, which more or less dissolved adheres `to the particles, especially the fine ones.

Apparatus according to the invention are illustrated in the accompanying drawings in which:

Figure 1 is a plan View of a machine for screening fibrous material.

Figure 2 is a secton on the line 2-2 of Figure 1,

Figure 3 is a section Figure l,

Figure 4 is a se'ction on Figure 1,

Figure 5 is 'a section in the direction of flow through a screening surface.

Figure 6 is a fragmentary section on the line 6-6 of Figure 5.

the line of be used with advantage, by`

on the line 3--3 ofY Vnumeral I0 indicates Figure '7 is a section on the line 1-1 of Figure v2.

Referring now to Figures 1, 2 and 3, reference atrough, in which a box II having its bottom I2 formed as a screen is partly immersed. The fibrous material is in the form of a suspension in the channel I3 and is supplied from the same to the box I I through the inlet I4. For the purpose of controlling the supply of the fibrous suspension a control shutter I5 is provided in the channel I3. Laterally of the box II and the trough I0 there are'provided two supports I6 and I'I. On the said supports and across the box II there are provided, in pairs, four channeled beams I8, I9 and 20, 2I respectively. Between the beams I8 and I9 there is a space, in which two tubular sleeves 22 and 23 are provided perpendicular to the longitudinal direction of the beams and rigidly connected to the beams by means of collars 24 and 25 respectively, welded one to each sleeve, which collars are united with the beams by means of bolts and nuts. Corr ndingly two tubular sleeves 26 and 2l are provided between the beams 20 and 2I. In each sleeve 22, 23, 26, 21 there are provided two coil springs 28 and 29 (see Figure 7, in which the sleeve 22 is shown in section). The upper spring 28 with its upper end rests against a spring holder 3U and'with its lower end against a cross piece 3l. The spring'v holder 30 rests against the screw 32, disposed in the cover 33, which closes the upper part of the sleeve 22. -The lower spring 28 with its upper part rests against the cross piece 3l and with its lower part against the spring holder 34. The latter is supported by a sleeve 35, screwed into a cover 36 provided in the lower part of the sleeve 22. In the cross piece 3| there is provided a pin 31 to which a bolt 38 is turnably suspended. The lower end of the said bolt 38 is mounted turnably about ya pin 39 provided in the side wall of the. box II as shown in Fig. 2. Thus, the box II is suspended at four points by coil springs. Through the side walls of the box II and journalled in two strong bearings 40 and 4I there is provided a shaft 42, which is driven by a motor 43 vlavthe clutches 4l and 48. On the shaft there are rigidly fixed two unbalanced members 44 and 45, i. e. bodies that have their centres of gravity eccentrically positioned in relation to the shaft 42. An unbalanced member of this type is shown in Figure 4 and consists of a circular unbalanced wheel, the eccentric position of the centre of gravity having been obtained by drilling a number of holes 46 in one half of thewheel. At the rotation of the shaft 42 the box II, on account of the unbalanced members will thus have a vibratory motion and each point of the same will move in an elliptic curve.

on account of the elastic suspension means. The amplitude of the oscillations may be made less or greater by changing the weights of the unbalanced members or the centres of gravity of said members. The tension of the springs 28 and 29 may be regulated by the screw 32 and the sleeve 35.

The apparatus operates in the following manner.

The suspension flowing in the channel I3 is continuously fed through the inlet I4 down into the box II. Due to the vibratory motion the screening is facilitated. The good fibrous material passes through the screening bottom I2 out into the trough I0 from where it is led away through the channel 49. The brous material, which does not pass through the bottom I 2 passes over the same and is led away through the channel 50.

As will be seen from Figure 2 the screening surface I2 has a bottom curved in the direction A in which the brous material is led. The part of 5 the suspension that has passed through the screening surface may be dammed up, so that the bottom of the box Il will be more or less immersed in the suspension.

The section of the screening surface, when 10 seen in the direction of flow, preferably consists of a broken or curved line, which rst extends steeply downwards and then, possibly with some transition, where the direction successively passes into a horizontal direction, a rather large part 15 of the whole extension of the screening surface in horizontal direction extends less steeply upwards, possibly with a continuation having horizontal or downwardly directed form.

An embodiment of the screening surface of such a-type is illustrated in Figure 5, from which it will be seen that the rst downwardly directed part of the section line consists of two approximately equal large zones A and B. The inclination of the zone A to the horizontal line may preferably be 70 to 30 and that of the zone B 30 to 0. 'Ihe part extending less steeply from the zone B also consists of two approximately equal large zones C and D, which preferably have an inclination to the horizontal line of 0 to +20o and +10 to +30 respectively. 'I'he latter part of the section line is continued, with a continuous bend, by a zone E, which may have an inclination of +15 to 0. After the zone E there may also be a downwardly directed part F., 'I'his 35 part is of importance in case it is desired that the material which does not pass through the screen surface, is to leave the same in the form of a coherent web.

The openings or perforations in the screen may 40 preferbly have limiting walls, which at least on part of the surface of the member are obliquely directed relatively to the surface of the screen. Such an oblique arrangement of the perforations is illustrated in Figure 6, in which the limiting walls of the screening perforations incline obliquely relatively to the screening surface 8|.

,Thus, by arranging the perforations inthe screen in such a manner that the limiting walls become obliquely situated relatively to the screening surface, it is possible to control the penneability of the screen within wide limits. In case the limiting walls 80 incline obliquely forwards,

when seen in the feeding direction, i. e. approximately in the direction of the major axis of the ellipse described by` each point of the vibrating screen the permeability is increased for suspended matter. If on' the other hand the limiting walls 80 incline obliquely backwards, when seen in the feeding direction, i. e. substantially in the direction of the minor axis of the ellipse described by each point of the vibrating screen the permeability is decreased for suspended matter.v

The limiting walls may also have diilerent inclination at different parts of the screen.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

In an apparatus for screening cellulosic pulp the combination of an elongated screen extending in the longitudinal direction substantially horizontally from an inlet at one end to an out let at the other end, and comprising in the direction of ow first a relatively short portion extending steeply downward, and then as continuation thereof a portion, everywhere inclining less steeply to the horizontal plane than the first portion and from a lowest point rising continuously to the outlet portion of the screen, elastic and substantially vertically yielding means connected to the two longitudinal sides of the screen for supporting the same, means for vibrating the screen united with the middle portion of the screen sides between the inlet end and the outlet end so that the inlet end as Well as the outlet endl of the screen perform orbital vibrations, and means beneath the screen for damming up liquid so that the screen will be at least partially surrounded by liquid on both sides.

NrLs WALFRID JNssoN. 

